Empty 30 lb. steel tank weighs 25 to 28lbs or about 10 lbs. more than a 20 lb. tank. So, a pair of full tanks would add 40 lbs to your tongue.
Then there is the storage box on the tongue, if you have one, and where the batteries are located, if you don't.
All things to consider.

Common 20-pound and 30-pound tanks are the same diameter and have similar collars, so the same brackets work, although typically with a longer threaded rod. If a tank cover is used, a taller one would presumably be needed.

oooh 30# tanks are tall. ETI is building trailers with the most efficient propane appliances possible for the size of the trailer. I'd carry a spare 20# tank for those "special times" before I'd permanently add more weight permanently (and the cost of those 30# tanks!). YMMV

Yes, 30-pound tanks are a lot more expensive than the very much more common 20-pound size. Also, if you don't have any special features in a 20-pound tank (such as a level gauge), it can be swapped for a full equivalent at a propane tank exchange, in case you can't find a bulk propane retailer.

I would rather have one tank, with a good gauge, which can be filled through a meter (paying for only the propane received) whenever desired - this would give the most useful capacity for the weight. This means a fixed-type tank (like motorhomes use) or a portable tank in the style used for forklifts; one FiberglassRV member set up his trailer with forklift tank, but I would not expect Escape to accommodate this as a customization, and the tank is expensive.

Donna,I like the way you think! Excellent alternative to replacing the original 20's with the 30's. Carrying an extra 20 is a way better idea the adding two heavy 30's. 30's are much more awkward to handle.

Empty 30 lb. steel tank weighs 25 to 28lbs or about 10 lbs. more than a 20 lb. tank.

I think more typical weights are 18 lb (for the 20-pound capacity) and 25 lb (for the 30-pound capacity) - the larger tanks are more efficient containers - but we're only talking a couple of pounds here... the added weight is certainly a factor.

We picked up our 19 in July this year and have used the trailer for three trips, one trip for 3 weeks, and have ran all our appliances including the furnace on propane and did a fair amount of cooking in the trailer and have yet to switch over to the second 20 lb tank - I think it getting close. I am thinking no rush in refilling that empty tank.